The present invention generally relates to a library unit, and more particularly, to a library unit in which a plurality of cartridge-type recording media (hereinafter referred to as cartridge disks) are stored in a respective cell and a desired cartridge disk is taken out from a cell by a cartridge disk carrying mechanism (hereinafter referred to as an accessor) when a recording and/or a reproducing of information of the medium is carried out.
A library unit, in which a plurality of cartridge disks are stored in a respective cell provided in a respective housing (hereinafter referred to as the frame), and a desired cartridge disk is taken out from a cell by an accessor, which runs through the center portion of the library unit, when a recording and/or a reproducing of information of the cartridge disk is performed, has been used. The cartridge may be returned to the original position (cell) by the accessor after the use.
In such a library unit, a method for positioning the accessor to a correct position of the cell is very important for carrying out proper handling of the cartridge disk. This positioning is often performed by using data of the mechanical structures, such as lengths of the frame in X, Y and Z directions (refer to FIG. 1 ) and a distance between each frame and the accessor, which are input in a memory in advance.
In a conventional library unit, however, there is a case that after carrying out a maintenance or an exchange of an accessor, such mechanical structures are changed and the data indicating a relative positional relationship between the accessor and each frame (cell) can no longer be used. In such a case, it is necessary to measure the relative positional relationships between the accessor and all the frames again. This procedure is of course tedious and time-consuming. Moreover, if an inclination of a shaft of an accessor has occurred after the relative positional relationships between the accessor and each of the frames are measured, the measurement of the positional relationships must be performed once again.
Also, in a conventional library unit, since no relative positional relationships are measured in back and forth directions of the accessor (i.e. the Z direction), no information is available about how far a picker (a cartridge disk holding portion) of the accessor should be moved in order to hold a cartridge disk in a cell. Thus, the picker must always be projected to a position where a holding of a cartridge disk is secured. For this reason, the picker is excessively projected when the position of a desired cell is closer to the picker than a calculated distance, and hits the back wall of the cell. On the other hand, there is a possibility that the picker misses holding the desired cartridge disk when the cell is far away from the picker portion of the accessor.
Moreover, when an entire structure of the plurality of frames is changed, for instance, due to an increment in a number of frames, it is necessary to renew the frame information input to a memory beforehand through an operation panel manually. Thus, if a mistake is made in inputting new information about the frame structures, there is a possibility that an access is made to a non-existing address or a system break-down is caused. Further, in a conventional library unit, when there is a change in a state of a frame, the relative positional relationship has to be measured again for not only the particular frame in which the change is caused but also for all the other frames. Thus, a substantial amount of time must be spent for the required relative positional measurement.
In addition, when a cell shelf comprising a plurality of cells is employed, it is necessary to make a relative positional measurement for all of the cells since a positional relationship or space existing in each cell is not constant. Thus, a number of cells subjected to a positional measurement is increased and, hence, it takes a long time to complete all the measurements.